(1) Field of the Invention
The present invention generally relates to methods and devices for modulating radiation, such as when a light beam is modulated to produce a color image. More particularly, this invention relates to a diffraction grating device with interdigitized elements that can be individually electrically addressable to diffract radiation of different wavelengths, and can be used in a variety of optical devices, such as a compact, reconfigurable full-color image source.
(2) Description of the Related Art
Devices with individual electrically-addressable elements have been considered for use in full-color, reconfigurable image sources, such as head-up displays (HUD's) in automobiles. Such devices generally provide a full color image source by modulating a light beam with the use of numerous pixels, each defined by an individual or set of modulating elements. For example, color images have been produced by reflecting light using a separate moveable mirror for each pixel, such as in U.S. Pat. No. 4,710,732 to Hornbeck. Individual electrically-addressable diffraction grating devices have also been considered. In U.S. Pat. No. 5,841,579 to Bloom et al., a light beam is modulated by periodically deforming a substantially flat reflective surface. The reflective surface has selectively deformable portions that provide a diffraction grating as a result of the deformable portions being biased out of the plane of the reflective surface, such that light modulation is achieved by diffraction.
Bloom et al. further disclose the use of multiple gratings per pixel, in which each grating within a pixel is configured to produce a different light color to effect a full color array. A disadvantage of pixels formed of multiple gratings is that they are necessarily larger than pixels containing only one grating. Another disadvantage is that any grating not being used to produce a specific color diffraction will be a dark space in the pixel. Additionally, a difficulty arises because each grating in the pixel must be addressable so that the desired color for that pixel can be attained. While addressing a grating can be easily accomplished using top side metal runners, at least two runner per grating is needed, each of which creates an undesirable dark space on the pixel. As the number of gratings per pixel is increased to enhance the full color effect, a greater number of runners is likewise required, such that an array of such pixels becomes more complex and difficult to address, and pixel density is decreased resulting in a lower resolution for the pixel array.
In view of the above, one can appreciate the need and difficulty of achieving a diffraction grating device capable of providing a compact, reconfigurable full-color image source that can be readily manufactured. Such a device would preferably overcome the shortcomings of the prior art by minimizing dark spaces, simplifying addressing and maximizing pixel density.